In vinegar production, there have heretofore been two possible ways of dealing with the accumulation of foam during the fermentation process. One way entails the use of a mechanical defoamer or foam breaker, with the separated liquid portion of the foam being recirculated back into the fermentation tank, while in the other way it is necessary to permit the accumulating foam to overflow into a seperate collecting vessel. In either case, however, the foam, after being clarified and filtered, ultimately has to be reused in the fermentation process, because the quantity of foam that is generated is simply too large to be disposed of. In the production of high percentage alcohol vinegar, the foam formation is in the first instance dependent on the operational qualities of the fermenter. If the fermenter runs so well that a substantial harming of the vinegar bacteria is avoided, relatively little foam will be generated. If the fermenter operation, on the other hand, is mildly defective, which will be the case with most fermenters and may, for example, be due to a less than ideal aeration or cooling of the fermenting liquid or a deficiency in the injection of mash into the fermenter, the resultant appreciable harming of the vinegar bacteria will lead to a substantial generation of foam. This in and of itself might still be tolerable and permit the fermenter to be run without the aid of a defoamer.
One can never fully exclude the possibility, however, that a complete breakdown of the fermentation could occur, caused, for example, by a relatively brief power outage or by a running of the fermentation at a zero percent alcohol concentration in the event of a malfunction of the alcohol feed system. Should that happen, almost all the vinegar bacterial will die suddenly and an extraordinarily high degree of foaming will result, with liquid constituting up to 50% of the foam and it being impossible to discern the boundary between liquid and foam in the fermenter. If this foam were to be vented to the outside of the fermenter in the absence of a mechanical defoamer, the entire contents of the fermenter would be transformed into foam and emptied out of the same in a relatively brief time interval. Thus, the use of a mechanical defoamer or foam breaker is absolutely essential in such a case, in order to control the high foam pressure created in the fermenter and to minimize the formation of foam.
It might be noted, in passing, that in the production of malt vinegar, wine vinegar and fruit vinegar, the use of a mechanical defoamer is always required, because such mashes inherently tend to foam since they are infected with bacteria which die in the fermenter.
In order to avoid the necessity of having to break up the foam accumulating in a fermentation tank during a vinegar fermentation process completely into a gaseous and a liquid portion, it is known from Austrian Patent No. 206,866 and its corresponding U.S. Pat. No. 3,262,252, the disclosure of which is incorporated herein by this reference, to withdraw the foam from the fermenter into an apparatus which includes a generally cylindrical housing arranged to be traversed axially by the foam, and a motor-driven rotatable member or rotor disposed in the housing and journaled for rotation about an axis parallel to or coincident with the axis of the housing, the rotatable member comprising a hub or axle carrying a plurality of radial vanes defining therebetween a plurality of circumferentially adjacent, axially extending, cross-sectionally generally V-shaped, open-topped passageways. Thus, as the foam moves axially through the housing, it is subjected, when contacted by the vanes of the rotating member, to centrifugal forces, which leads to a radially outward displacement of the liquid portion of the foam and a separation thereof from the main gaseous portion and permits the gas to be axially withdrawn from the rotating member and the housing both liquid-free and foam-free. The liquid portion, which is so denoted even though it may still have some foam remnants (herein referred to as foam particles) attached to it, is removed through a liquid discharge outlet in the housing wall and is recycled into the fermentation tank for remixing with the fermentation substrate, in connection with which an unobstructed circuit for foam movement between the fermenter and the rotatable member is established in order to obviate having to undertake a complete, high energy-consuming, break-up of the foam into separate gaseous and liquid portions.
This circulation of the liquid portion of the foam back to the fermenter has proved to be satisfactory in regularly conducted fermentation processes but, when something interferes with the smooth running of the process, can lead to an excessive foam buildup, so that the drive motor for the rotating member becomes overloaded and the foam break-up is interrupted, which in turn can ultimately lead to an interruption of the entire fermentation process. Such an excessive foam build-up can, by way of example, occur during a submerged vinegar fermentation if the vinegar bacteria are damaged by virtue of an insufficiency in the oxygen supply, a too rapid change in either the alcohol concentration or the acetic acid concentration, or an operator's error.